A red laser and a blue laser deliver the same beam intensity (same power per unit area). Which statement correctly compares their photons?
ABlue photons have more energy per photon and there are more of them per second
BRed photons have more energy per photon because red light carries more heat
CBlue photons have more energy per photon, but fewer blue photons are emitted per second than red photons at equal intensity
DRed and blue photons have the same energy since intensity is equal
Photon energy depends on frequency: E = hf. Blue light has higher frequency than red, so each blue photon carries more energy. But intensity is total power per area — if the blue beam delivers the same power with higher-energy photons, it must emit fewer photons per second to compensate. This directly targets the misconception that intensity determines per-photon energy.
Question 2 True / False
When light travels through glass (apparent speed c/n), each individual photon is slowing down from c to c/n inside the glass.
TTrue
FFalse
Answer: False
Photons always travel at c in vacuum between interactions. The apparent slowing in a medium results from photons being absorbed and re-emitted by atoms in the material. The light pulse as a whole travels at c/n, but each individual photon moves at c between those absorption/re-emission events.
Question 3 Short Answer
Explain why the classical wave model of light was insufficient to explain the photoelectric effect, and what the photon model adds.
Think about your answer, then reveal below.
Model answer: The classical wave model predicts that increasing intensity (at any frequency) should eventually eject electrons, since energy builds up continuously. But experiment shows that below a threshold frequency, no electrons are ejected regardless of intensity. The photon model resolves this: ejection requires a single photon with energy E = hf exceeding the metal's work function. Intensity controls how many photons arrive per second, not their individual energies.
This gets at the core reason the photon model was necessary: energy transfer is quantized, not continuous. A billion low-frequency photons cannot eject a single electron if none individually has enough energy to overcome the work function. The photon model explains this directly; the classical wave model cannot.